Many years ago when I lived in Mexico City, I took a day trip to Teotihuacan with an old friend who was visiting from the U.S. We were typical tourists, strolling around the site with a guide, climbing to the top of the Pyramid of the Sun with a crowd of people, wading through the swarm of vendors to buy souvenirs. I couldn't have imagined for a moment that fate would bring me back under far different circumstances.

To research this story, I stayed at a small hotel near the ruins. I rose at dawn and got to the site before anyone except the guards and was able to walk the length of the Street of the Dead, the main thoroughfare, accompanied by the song of birds. At the far end of the avenue stood my destination, the Pyramid of the Moon. Over the course of the next few days, I climbed its staircase countless times to reach the archaeologists' access tunnel high on the south side. And on several occasions I was allowed to duck down through the tunnel to see them at work—excavating, drawing, and photographing one of the sacrificial burials deep inside the massive stone structure. It was an awesome, once-in-a-lifetime experience.

What was your worst experience in the field covering this story?

Plunging into an ancient pyramid in earthquake country? Not a problem. It was climbing the tall stone structure that threw me. The archaeologists' tunnel descended into the pyramid from one of the upper terraces, and clearly I was going to have to get myself up there. Don't look down. Don't look down, I chanted to myself as I climbed the narrow, steep steps, past groups of tourists sitting halfway up, under the barbed wire with the "Do Not Enter" sign, and up one more flight. Finally, I was on the wide, flat terrace with a view of the whole length of Teotihuacan's main thoroughfare. OK, great. But I still had to get back down. Stepping over the lip of the terrace into what seemed at first like nothingness was stomach churning. I focused on each step, avoided looking at the ground far below, and arrived at the bottom safely—if slowly. After many round trips during the course of our work, I figured out the easiest way to get up and down: stepping sideways onto the stairs and taking a diagonal route. I never felt completely comfortable, but by the end of my visit I could move pretty fast.

What was your quirkiest experience in the field covering this story?

My visit to Teotihuacan coincided with the last days of the last field season at the Pyramid of the Moon, the end of six years of excavation carried out mostly by Mexican and Japanese archaeologists. It was a time of despedidas—goodbye parties—celebrating the camaraderie that comes from working long and hard and well together. I was leaving the same day as Yuko, a Japanese graduate student, and the team planned a send-off for both of us the night before. In the dig house, with Yuko still bent over a drawing she needed to finish, we made our first toast with tequila, and then another with sake from a beautifully wrapped and obviously very special bottle. As we sipped and munched chips and other snacks from the local market, our polyglot conversations somehow turned to the noises that animals make in Spanish, English, and Japanese. "Koh-key-koh-KOH," we crowed like roosters in Japan. "Wow-wow," we barked like dogs in Mexico. We lingered, savoring the laughter, until long after such creatures of the day had gone to sleep at Teotihuacan.